There has been a proliferation and overlapping in recent years of different types of relatively complex aircraft radio navigation systems, and this proliferation has lead to excessive costs in the aircraft as well as the ground stations. Also, the present and developmental landing guidance systems lack versatility and capabilities needed in coming decades. Furthermore, there is pressing need for an improved air traffic control system, in particular the inclusion in such a system of an effective collision avoidance system. There is a need, therefore, for a relatively simple and relatively inexpensive system which is capable of performing all these required functions. The system of the present invention answers these requirements, and is capable of providing, for example, the following functions:
1. Discretely addressed air traffic control (ATC) surveillance;
2. Precise terminal and enroute area navigation with accuracies more than an order-of-magnitude better than the conventional VORTAC system, including pilot selectable automatic Standard Terminal Area Route and Standard Instrument Departure guidance in the terminal areas;
3. Precise distances for landing guidance;
4. Precise landing guidance, including automatic flare guidance, which is not accomplishable with existing microwave landing systems (MLS);
5. A single ground facility capable of providing multi-runway guidance;
6. A high speed two-way data link;
7. Collision warning/avoidance data provided at a high continuous rate in terms of traffic positions for pilot display/avoidance and/or ground-computed escape maneuvers, including accuracies adequate for horizontal as well as vertical escape maneuvers; and
8. With auxiliary programming, an automatic airport terminal in lieu of a manned control tower.
The system of the invention includes a series of ground stations located at the various airport terminals, and at selected points along the various aircraft routes. Vertical guidance and associated coding are included only in the terminal facilities. Thus, a typical airport terminal facility incorporating the concepts of the present invention is capable of accomplishing the functions of an ATC surveillance interrogator, a VOR/DME, and an instrument landing system (ILS), with greater capabilities than any of the prior art systems.
The DABNLS is a multi-phase coded pulse system, and the system utilizes steeply rising leading edges for the pulses to permit precise timing for precise distance measurements. The system of the invention also includes computational facilities at the ground station which provide position coordinates (latitude and longitude) and also off-set course deviation and distance data transmitted to the aircraft for area navigation guidance.
The computational facilities of the ground stations of the system of the invention at the various terminals also provide three-dimensional position off-sets for landing guidance of the aircraft to multiple runways of the airport. The computational facilities serve to provide horizontal and vertical "course softening" off-sets as the aircraft approaches the runway. The computation facilities also provide automatic flare guidance to the aircraft, utilizing wheel-to-antenna height and other data received from the requesting aircraft.
The ground stations also include an air traffic control surveillance function which utilizes the discretely addressed omni-directionally transmitted interrogation pulses, and an interferometer receiving antenna sub-system for determining the aircraft bearing from the reply pulses, the combination providing more flexible aircraft interrogation scheduling, higher continuous replay rate, and more effective reflection suppression than is possible with the scanning beam and complex reflection suppression networks used in present-day radar beacon systems.